Helianthemums, or rock roses, are charming little evergreen plants, with wiry prostrate stems, and small flowers, which are freely produced all the summer. They may be had in white, yellow, pink, scarlet, and crimson, and either double or single; the variety named Mrs. C. W. Earle is a very effective double scarlet, and quite a novelty.
Iris reticulata is a very fascinating little bulbous plant, well adapted for a rockery; it blooms in the early spring, and very beautiful the flowers are, being rich violet-purple, with gold blotches on each petal; they are scented, too; when in blossom, the stems reach to about nine inches in height.
One of the most lovely plants that can be imagined for a rockery is lithospermum prostratum, and yet how rarely one sees it; the glossy green leaves always look cheerful, and the flowers are exquisite, they are a bright full blue, and each petal is slightly veined with red, it is not difficult to grow, a dry, sunny position being all it requires; it is of trailing habit and an ever-green. Everyone knows the creeping jenny, but it is not to be despised for rock-work, especially for filling up odd corners where other things will not thrive. It blooms best where there is a certain amount of sun.
St. Dabeoc’s Heath is a pretty little shrub, very neat and of good habit; its flowers are the true pink, shading off to white, and of the well-known heath shape. Somewhat slow-growing, it prefers peat.
Plants that flower the whole season through are most valuable on the rockery. Œnotheras may be depended on to present a pleasing appearance for several weeks, especially if all dead flowers are picked off. The dwarf kinds are the most suitable, such as Oenothera marginata, missouriensis, linearis, and taraxacifolia. The last-named, however, is only a biennial, but has the advantage of opening in the morning, while most of the evening primroses do not seem to think it worth while to make themselves attractive till calling-hours.
The most fairy-like little plant for filling up narrow crevices in sunny quarters is the dear old wood-sorrel. It has tiny leaves like a shamrock in shape, but of a warm red-brown colour, and the sweetest little yellow flowers imaginable; they are borne on very short stalks, and only come out when the sunshine encourages them; the whole plant does not exceed three inches in height; it spreads rapidly, seeds freely, and thrives best in a very light soil; it will also do well on walls.
The alpine poppies are so delicate and graceful that they seem made for the rockery. They only grow six inches high, and continue in flower at least four months; they may be had in a great range of colours, and are easily brought up from seed. Nice bushy plants can be had of these poppies for about four shillings a dozen, and it is needless to say they require plenty of sunshine. The word phlox conveys to many people the idea of a tall autumn-flowering plant, with large umbels of flowers, individually about the size of a shilling. But these are not the only species; the alpine varieties are just as beautiful in a different way, though some are not more than a few inches high, and each flower no bigger than a ladies’ glove-button. In spring and early summer they become perfect sheets of bloom, so that the foliage is completely hidden; when out of flower, they are soft green cushions of plants, and serve to cover bare bricks well.
The alpine potentillas are pretty, and keep in flower for a long time. P. nepalensis is a good one, but the merits of p. fruticosa are much exaggerated, its dirty-looking yellow flowers are by no means prepossessing.
No rockery is complete without several specimens of the family of saxifrages. One cannot do better than make a beginning with them, as they are so fine in form and diverse in style. S. aizoon compactum is one of the best rosette species, and S. hypnoides densa of the mossy tribe; other kinds well worth growing are S. burseriana, which has pretty white flowers on red hairy stems in early March; S. cunifolia, with charming fresh pink blossoms, and of course S. umbrosa, the sweet old-fashioned London pride. A dry sunny situation suits the saxifrages best.
The House leeks are somewhat similar in appearance, but like drier situations than the last-named plants. The sempervivums delight to creep along a piece of bare rock, and one marvels how they can derive enough sustenance from the small amount of poor soil in which they are often seen growing. The cobweb species, called arachnoideum, is most interesting, and invariably admired by visitors; it has greyish-green rosettes, each one of which is covered with a downy thread in the form of a spider’s web. A kind more often seen is sempervivum montanum, and certainly it is a very handsome species, with curious flowers supported on firm succulent red stems. It is to be seen in broad clumps at Kew, and very well it looks.